1. Field of the Invention
The present invention relates to an image density adjustment method for image forming apparatus of the electrophotographic type.
2. Description of the Related Art
In conventional copiers and printers of the electrophotographic type, a test pattern image of constant area is formed on the surface of a photosensitive drum and the density of this test pattern image is optically detected, and the charge voltage of the photosensitive member, developing bias voltage, and amount of optical exposure is changed in accordance with said detected density value so as to maintain an optimum image density. This control is based on changing the optimum image forming conditions to maintain a constant image density by changing the environmental conditions which to compensate for fatigue of the photosensitive member and developer (carrier) over time. Developer is particularly susceptible to fluctuation of environmental conditions and developing capability is markedly reduced under conditions of high temperature and high humidity. Since image density is naturally reduced if developing capability is reduced, the charge voltage or toner density must be increased.
When adjustment of the charge voltage of the photosensitive member and adjustment of the toner density are compared, it can be understood that adjustment of the charging voltage is advantageous inasmuch as it provides excellent responsiveness to image density, but is disadvantageous insofar as optical exposure becomes inadequate due to the decrease in potential of the background area of the photosensitive member in conjunction with the increase in charging voltage. Optical exposure cannot be set too high from the perspectives of additional power consumption of the lamp, temperature elevation, and service life of the lamp and photosensitive member. On the other hand, whereas adjustment of toner density does not produce the aforesaid disadvantage of inadequate optical exposure, it is nevertheless disadvantageous in that responsiveness to image density is delayed because the toner density changes only gradually, and when toner density is increased beyond necessity, toner adheres to non-image regions and causes image noise.